From: "F. Senault" <fred@...>
Date: 2010-05-18T20:45:13+09:00
Subject: Re: Opening a stream to multiple (possibly zipped) files

Le 18 mai � 08:11, Martin Hansen a �crit :

>> Maybe you could reimplement the Perl code trying to decompress always
>> and trapping the exception when the file is not compressed? Something
>> like this:
>> 
>> irb1.9 -rfacets/zlib -rzlib -rstringio
>> irb(main):001:0> Zlib.decompress("plain text")
>> Zlib::GzipFile::Error: not in gzip format
> 
> That is a good idea (I don't think you can rescue exceptions in Perl). 
> However, I am still uncertain if wise/possible and how to get a single 
> file handle on a stream from multiple files. I need to do 
> zipping/unzipping on the fly since I want to work on huge files.

This should work :

require "zlib"

def openf(fn)
  File.open(fn) do |f|
    sig = f.read(3)
    f.rewind
    if sig.bytes.to_a == [31, 139, 8]  # GZip file signature
      gz = Zlib::GzipReader.new(f)
      yield gz
      gz.close rescue nil
    else
      yield f
    end
  end
end
      
>> openf("toto.gz") { |f| puts f.read }
aljezalkezajlkezaj
=> nil
>> openf("toto2.txt") { |f| puts f.read }
iappoeipozaipza
=> nil

(You'd want to work on the exception handling etc, of course.)

Fred
-- 
Although I may flirt    With all kinds of dirt   To the point of disease
Now I want release        From all this decay               Take it away
And somewhere        There's someone who cares      With a heart of gold
To have and to hold                  (Depeche Mode, To Have and to Hold)